Capsid protein and helper component-proteinase function as potyvirus cell-to-cell movement proteins

Area of Science:

• Plant Virology
• Molecular Plant Pathology
• Virus-Host Interactions

Background:

• Potyviruses, a large genus of plant viruses, rely on specific viral proteins to move between plant cells.
• Viral movement proteins (MPs) are crucial for overcoming plant cell barriers, primarily through plasmodesmata.

Purpose of the Study:

• To investigate the roles of specific bean common mosaic necrosis virus (BCMNV) and lettuce mosaic virus (LMV) proteins as viral movement proteins (MPs).
• To determine the functional domains within the capsid protein (CP) and helper component-proteinase (HC-Pro) essential for viral cell-to-cell movement.

Main Methods:

• Expression of recombinant proteins in Escherichia coli.
• Microinjection of purified proteins into plant cells.
• Analysis of protein trafficking, plasmodesmal gating, and viral RNA movement.
• Site-directed mutagenesis and deletion analysis of CP and HC-Pro.

Main Results:

• Both potyviral capsid protein (CP) and helper component-proteinase (HC-Pro) demonstrated MP activity, trafficking between cells, increasing plasmodesmal size exclusion limit, and facilitating viral RNA movement.
• Mutations within the core region of CP and C-terminal deletions in HC-Pro significantly impaired or abolished cell-to-cell movement.
• Other BCMNV proteins (P1, CI, NIa, NIb) did not exhibit MP properties, though NIa and NIb accumulated in the nucleus.

Conclusions:

• The study provides direct evidence for the multifunctional roles of potyviral CP and HC-Pro as viral movement proteins.
• Specific domains within CP and HC-Pro are critical for mediating cell-to-cell transport, highlighting their importance in the potyvirus life cycle.